We know from seismic wave data that the inner core is soft, with a low shear-wave velocity, meaning it can't just be solid iron or iron alloy. Some scientists think there could be a second inner inner core, while others think that due to the lighter density than would be expected by pure iron alone, there could be some light elements as an alloy. But a new study, led by Yu He from the Chinese Academy of Sciences, has now investigated the potential phase of matter this mix of elements may exist in down, arriving at the suggestion that the...